Chlorination of paraffinic hydrocarbons



Patented Oct. 19, 1948 'CHLORINATION OF PARAFFINIC HYDROCARBONS EverettGorin, Dallas, Tex., assignor, by mesne assignments, to Socony-VacuumOil Company, Incorporated, New York, N. Y'., a corporation oi New'YorkApplication January 26, 1946, Serial'No. 643,800

Claims. (Cl. 260-659) This invention relates to a process for the-chlorination of normally gaseous hydrocarbons, The invention isconcerned particularly with the production of chlorides of methane frommethane and dry natural gas, 1. e., a natural gas from which most of theethane and substantially all of the propane and higher molecular weighthydrocarbons have been removed.

Vast quantities of methane are available in the form of natural gas, thechief use of which has been its utilization as a fuel. A considerableamount of the supply is used to produce carbon black. More recentlyattempts have been made to increase the production of fuels for internalcombustion engines by converting methane to normally liquid hydrocarbonsin such synthetic processes as th Fischer process and modifications ofthis process and new processes have been proposed for using methane as astarting material for the production of chemical intermediatesby'oxidation and chlorination processes.

,Various methods have been proposed for the chlorination of normallygaseous hydrocarbons, such as methane, to form therefrom thecorresponding alkyl and alkylene chlorides. The conventlona1 method ofdirect chlorination with free chlorine has been used for many years.However, this method has several disadvantages which have not beenentirely overcome. The reaction of free chlorine with methane is highlyexothermic and hence the reaction is very dimcult to control at moderatetemperatures and explosive mixtures of the reactant gases are difficultto avoid, Also large volumes of hydrogen chloride are formed in thedirect chlorination process and since the reutilization of the hydrogenchloride in the chlorination process is of primary importance to makeany hydrocarbon chlorination process economically feasible, it becomesnecessary to incorporate with th process a coordinating chlorinerecovery process such as the Deacon process.

The primary object of this invention is to produce chlorides of methane.Another object of the invention is to provide a continuous process forthe chlorination of methane and natural gas wherein the chlorinationreaction is readily controlled. Another object of the invention is toprovide a continuous process for the chlorination of methane and naturalgas wherein the hydrogen chloride produced by such chlorination isutilized in producing chlorinating agent for the process. A furtherobject of the invention is to provide a continuous vapor Phase processfor the chlorination of methane and natural gas wherein explosivemixtures of free chlorine and the hydrocarbons undergoing chlorinationare avoided. -Other objects of the invention will appear hereinafter.

I have found that mercuric chloride may be reacted in the vapor phasewith methane and natural gas to produce monochlorides and higherchlorinated derivatives of these gaseous hydrocarbons. The reaction ofmercuric chloride with methane may be represented by the equation Theabove reaction takes place at temperatures ene are formed instead of thecorresponding hydrocarbon chlorides. The natural gas used in my processmust therefore contain only a limited amount of higher hydrocarbon, thatis, preferably less than 15 mole percent of ethane and not more than 2or 3 mole percent of propane. The conversion of normally gaseoushydrocarbonsto aromatics at temperatures above 600 C. in the presence ofvolatile metallic chlorides, such as mercuric chloride, is taught andclaimed in my copending application entitled Conversion of normallygaseous hydrocarbons, Serial Number 400,- 296,'flled June 28, 1941, nowU. S. Patent 2,396,- 697. In converting mixtures oi. mercuric chlorideand normally gaseous hydrocarbons to aromatics, the mercuric chloride iscompletely reduced to mercury in thechlorination-dehydrochlorinationprocess. I

I prefer to operate the herein described process of converting methaneto chlorinated methane at temperatures within the range oi! from about525 C. to about 575 C. under conditions of contact time describedhereinbelow such that no more than per-cent of the mercuric chloride isreduced to mercury and only minor amounts of the chlorinated hydrocarbonis reconverted to hydrocarbons. I have found that it contact timessubstantially greater than those required to reduce about 90 percent ofthe mercuric chloride are employed the ultimate product consistsprimarily of hydrocarbons and not chlorinated methane.- Ii. contacttimes below those required to obtain about 35 percent reduction of themercuric chloride are employed the concentration of chloromethanes inthe product gas is too low to permit their economical recovery. I haveobserved that when contact times within the range seconds are employed,35 percent to 90 percent of the mercuric chloride is reduced. In theabove expression T is the degrees Kelvin maintained in the reactionzone. Thus, for operation at a temperature of 525 C. the proper range ofcontact time is from about 32 seconds to about 322 seconds and foroperation at 575 C. the range of contact time is from about seconds toabout 50 seconds, that is, an overall range of contact time of fromabout 5 seconds to 322 seconds for my preferred operating temperatures.The term contact time as used in this specification and in the claims isdefined as the reciprocal space velocity and is equal to the totalvolume of the reaction zone free space divided by the volume of reactantgases, reduced to standard conditions of temperature and pressure,passed therethrough per second. Contact time of the reactant gases inthe chlorination zone as defined herelnabove is greatly reduced whenoperating at elevated pressures. The chlorination reaction may becarried out at pressures from atmospheric to about 200 pounds gage,preferably about 150 pounds gage. However, the pressures are in allcases maintained sufflciently low so that the reaction is carried outunder vapor phase conditions.

The endothermic reaction of mercuric chloride with methane to formmethyl chloride is of particular utility since the by-product mercuryand hydrogen chloride can be reacted in the presence of oxygen or oxygencontaining gases to reform mercuric chloride chlorinatin agent. Thisreaction is exothermic and furnishes an excess of heat over thatrequired to chlorinate methane with the mercuric chloride agent. Thereaction of mercury with hydrogen chloride and atmospheric oxygen toform mercurous chloride takes place at temperatures from about 50 C. toabout 250 C. accordin to the equation The mercurous chloride dissociatesto produce free mercury and mercuric chloride at a temperature of about250 C. or above. The reaction between mercury, hydrogen chloride andoxygen may be carried out at temperatures above 250 C. to form mercuricchloride directly according to the equation In my process I prefer toregenerate mercuric chloride under conditions of temperature andpressure approximating temperature and pressure conditions in thechlorination zone.

The process of chlorinating methane by means of mercuric chloride may becarried out either batchwise or as a'continuous process. Thus, by theuse of a multiplicity of towers packed with material having a highspecific heat, that is, high heat capacity, the heat produced in theregeneration of mercuric chloride may be stored in the packing and bysuccessively alternating the chlorination andregeneration reactions inthese towers a part of the heat of regeneration may be most efflcientlyutilized in the chlorination process. 'Such a continuous regenerationmethod which is coordinated with a process for chlorinating methane orhydrocarbon mixtures consisting essentially of methane with only a minoramount of ethane is described hereinbelow. These mixtures which may bechlorinated by my process are obtained from a dry natural gas'from whichsubstantially all of the hydrocarbons having more than two carbon atomsper molecule have been removed.

Referring to the drawing, towers I and 2 are used alternately as methanechlorination zones 'and regeneration zones. These towers are packed ilyto the reactant gases in the chlorination cycle.

Suitable materials are quartz and relatively nonporous carborundum. Thepacking may be disposed in a series of beds as indicated or the packingmay be continuous in the towers. Towers 3 and 4 which are used torecover residual mercuric chloride vapors and mercury from the gaseouseilluent of the chlorination cycle are also packed with inert packinghaving the above properties.

The packing in these towers should be relatively porous in order toadsorb the mercuric chloride and hence I prefer to use porous packingsuch as porous carborundum or crushed fire brick in towers 3 and 4.

Methane in lin It) is passed by means of compressor ll through coil I2in furnace ii! at a pressure of about 150 pounds per square inch. Moltenmercuric chloride in line I6 is passed by means of pump IT to coil 3 infurnace 13. In furnace I3 the streams of methane and mercuric chlorideare raised to a temperature within the range of from about 525 C. toabout 575 C. vaporized mercuric chloride in line passes to methane line2| and the mixed vapors pass to manifold line 22 which leads to reactori. Valves 23 and 24 in line 22 are maintained in the open position topermit free passage of the gas to reactor I while valve 25 in line 26and valve 21 in line 28 are closed as is also valve 29 in line 22. 1

The mole ratio of methane to mercuric chloride introduced to reactor 1should be within the range of from about three to one to about ten toone. An excess of methane is preferable in order to obtain maximumconversion of mercuric chloride to methyl chloride product and minimumformation of the higher chlorinated derivatives of methane. A high ratioof methane to mercuric chloride also prevents the condensation of themercuric chloride and mercury product vapors. As the mixed vapors passupward in tower l' they contact the hot packing material which has beenheated in a previous regeneration cycle and the reaction indicated by 1)produces a gaseous mixture consisting of chlorinated methane, unreactedmethane, hydrogen chloride, vaporized metallic mercury and unreactedmercuric chloride vapor. With valves 36 and 36 in line 31 in the openposition and valves 38, 39, and 40 in lines 4!, 42, and 43 respectivelyclosed, the vapor product passes overhead through line 44 to condenser45. In condenser 45 the mercury and unreacted mercuric chloride vaporsare condensed and the mixed product of non-condensed product gases andliquid mercury and mercuric chloride passes through line 40 to hotsettler II. Settler 4'7 is operated at a temperature of from about 2'75C. to 300 C. and at a pressure substantially the same as reactor I, thatis, about 150pounds gage, and the metallic mercury and liquid mercuricchloride settle therein to form two liquid layers, the liquid mercuricchloride being supported by the liquid mercury. The liquid mercuricchloride is recycled to furnace l3 through line 48. Liquid mercury iswithdrawn from settler 41 through line 40 and transferred to heater 60by means of pump 5|. The liquid mercury is vaporized in heater 60 andthe vaporized mercur passes therefrom through line 62 to line 53 throughwhich reactant gases for the regeneration of mercuric chloride pass totower 2 described hereinbelow.

The gaseous effluent from settler consisting of unreacted methane,chlorinated hydrogen chloride, and small amounts of mercuric chlorideand mercury vapor pass overhead through valved line 80 to cooler 6|where the temperature of the gaseous mixture is lowered to the range ofabout 60 C. to 100 C. to condense out anyresidual mercuric chloride andmercury. The mixture is passed through line 62 to manifold line 63 andthence by line 64 to packed tower 3. valve 85 in line 84 being in theopen position. Valve 61 in line 69 and valve II in line 12 are closed Inorder to isolate tower 3 from gaseous stream passing to tower 4. Intower 3 suspended solid mercuric chloride is deposited on the packing.With valves I5 and 11 in lines I8 and 80 respectively closed, and valve8I in line 82 open the mixture of product gases and a small amount ofmercury pass through line 84 which leads to liquid mercury sump 05 fromthe bottom of which any residual mercury is passed throu h line to line49. The gaseous product passes overhead from sump 85 through valved line81 to absorber 90.

In absorber 90 the gaseous product mixture is contacted countercurrentlywith a stream of hydrogen chloride-water azeotrope containing from 20 to25 percent hydrogen chloride introduced to absorber 90 through line 9|by means of pump 92. The absorber is operated at pressures inexcess of100 pounds gage and the azeotrope removes hydro-gen chloride from thegaseous mixture. The solubility of methyl chloride and other chlorinatedmethanes in the azeotrope is slight compared with that of hydrogenchloride and the azeotrope rapidly becomes saturated with thehydrocarbon chlorides after which further absorption of the hydrocarbonchloride product practically ceases. The hydrogen chloride enrichedazeotrope passes from the bottom of absorber 90 through valve 93 in line94 to fractionating tower 95 which is equipped with heating means 95 andtop cooling means 91. Hydrogen chloride passes overhead fromfractionator 95 to the regeneration zone 2 through line 98 which leadsto line 50. If desired, the hydrogen chloride may be scrubbed withsulfuric acid to remove any water vapor before recycle to tower 2.Hydrogen chloride from an external source is introduced to line 53through line 99. Lean azeotrope passes from the bottom of fractionator95 through line I00 to cooler IOI and thence through line I02 to line 9Ifor reuse in absorbing hydrogen chloride from the product gas.

The gaseous product from absorber 90 consisting essentially of unreactedmethane and chlorinated methane passes overhead through line I toabsorber -I08 wherein the gas is contacted countercurrently with asuitable solvent for the aetresi chlorinated hydrocarbon such as apetroleum.

naphtha fraction. A relatively high boiling, narrow cut kerosenefraction or mineral seal oil may be used or a, chlorinated hydrocarbonsuch as car- 5 bon tetrachloride may be used as the absorbent liquidintroduced to absorber I06"through, line I0! by means of pump I08.Absorber I00 is operated at pressures in excess of 100 pounds per squareinch gage and as the absorbent descends 10 in the tower the chlorinatedmethane is absorbed from the product gas stream. If desired, towers I06and 90 may be packed with suitable inert packing in order to obtain moreefficient contact of the gas with the liquid absorbent. Unabsorbedmethane passes overhead from absorber I06 through recycle line I09 whichjoins methane feed line Ill. The chlorinated methane enriched absorbentis withdrawn from absorber I06 through line III] and passes throughvalve III 2" to fractionator II2 which is equipped with bottom heatingmeans H3 and top cooling means II4. Lean absorbent is Withdrawn fromfractionator II2 through bottom drawoif line H5 and passes via coolerIIBand line II! to absorbent feed line I01. Chlorinated methane passesoverhead from fractionator II2 through line II8. If desired, thechlorinated product may be withdrawn as a side stream from fractionatorII2 (not shown) reserving top drawoff line I I0 for the elimination fromthe product of any trace of methane picked up by the absorbent inabsorber I06 when operating the same at high pressure.

The regeneration of mercuric chloride reagent :5 by means of mercury,oxygen, and hydrogen chloride according to Equation 3 above isaccomplished in tower 2 while tower I is in operation on thechlorination cycle as described hereinabove. Reaction tower 2 afterbeing withdrawn 1:) from the chlorination cycle must be purged ofhydrocarbon gases before inauguration of the regeneration cycle. Withvalve I 20 in line 28 and valve I2I in line 42 open and valves I22 andI23 in lines 22 and 43 respectively closed, reactor 2 i5 is purged bymeans of hot flue gas introduced to the reactor through lines I24, 20,and 22, and the purge gas passes from reactor 2 through lines 43, 42,and I26. Following the purging of tower 2 valves I20 and I2I are closed,valves I22 and I29 are opened and Valves I26 and l2l in lines 26 and 4|respectively are set in the open position, thus preparing the inlet andoutlet manifold lines to reactor 2 forthe regeneration cycle which isdescribed below.

Following the deposition of solid mercuric chloride on the packing intower 4 the recovery of the solid mercuric chloride isaccomplished inthe following manner. Valve I32 in line I2 and valve I33 in line 18 areopened. Valve I34 in line I35 0 which connects with hot methane feedline 2I is now opened and part of the hot methane from furnace I3 ispassed through lines I35, I2, and 68 and thence through tower 4 andlines 80, I8, and I36 back to furnace fed line I0. The hot methanevaporizes the mercuric chloride and carries the vapors back to thechlorination cycle. The extent to which the packing is raised intemperature by the hot methane purge will depend on the length of timenecessary to remove the deposited mercuric chloride. Since the amount\of mercuric chloride deposited is usually small, the duration .of thehot methane purge will be relatively short. When it becomes necessary tocontinue the hot methane purge for sufllcient time to heat the packingin tower 4 to a relatively I high temperature in order to vaporizesubstantially all oi the mercuric chloride the heat stored in thepacking in the heating step may be recovered and the temperature oi thepacking may be lowered to mercuric chloride adsorption temperatures bypreheating cold methane passing to furnace ii. In order to lower thetemperature oi the packing, valve I34 in line I35 is closed erationcycle, a free oxygen containing gas such as air is introduced to theprocess through valved 'line I50 which connects with line 53. Asindicated hereinabove, hydrogen chloride is introduced to line .53through lines 98 and 09 and mercury is introduced to line 53 from line49. Makeup evaporated and the recovered mercuric chloride is returned tothe chlorination cycle. The mercury recovered from the cooled gas isreturned to the regeneration cycle.

The iollowing example illustrates the chlorination step oi my process. L

A gaseous mixture consisting oi methane and vaporized mercuric chloridein the mole ratio oi about five moles oi methane per mole oi mercuricchloride was passed through a Pyrex glass tube at X a temperature oi 530C. ior a contact time oi mercury is introduced to line 48 through lineI5I.

If desired, the mixture oi air, hydrogen chloride, and mercury vapor inline 53 may be raised in temperature by passing themixture in heatexchange with the overhead product from reactor I in line 44. The amountoi preheat given to this mixture will depend on heat losses fromregeneration reactor 2. In any case the temperature oi the mixture as itenters reactor 2 is sufiiciently high to avoid {condensation oi mercuryvapors from the mixture. The proportion of oxygen and mercury in themixture should be such that at least one mole of oxygen and two atoms oimercury are furnished respectively for each four moles of hydrogenchloride. I prefer to use at least 10 percent excess of mercury overthat required by stoichiometrlc proportions as indicated by Equation 3above in order that the hydrogen chloride may be substantiallycompletely oxidized.

The gaseous mixture from line 53 is passed by compressor I52 throughlines I53, 4|, and 43 to reactor 2 at a pressure within the range oifrom atmospheric to about 200 pounds per square inch, preferably about150 pounds per square inch. The temperature, which increases in reactor2 due to the exothermic nature of the reaction, is maintained within therange of irom about 500 C. to about 650 C.

The reaction product from regeneration reactor 2 passes through valveI22 in line 22 and through valve I28 in line 20 to line I54 leading tocondenser I55 where the temperature is lowered to the range of fromabout 275 C. to 290 C. or 300 0., and the mixture of liquid mercuricchloride, water vapor, oxygen depleted air, and unreacted mercury passesthrough line I56 to the mercuric chloride recovery zone. In the mercuricchloride recovery zone the mixture is introduced to a settler similar inoperation to settler 41 from which liquid mercuric chloride is passed byline I60 to line 48 and thence to mercuric chloride feed line I6 leadingto iurnace I3.

Liquid mercury is recycled from the settler in the mercuric chloriderecovery zone through line IBI to line 06 which leads to mercury recycleline 49. Mercuric chloride, hydrogen chloride, and mercury in the oilgas from the settler may be recovered by cooling the gas to about 100 C.and passing the cooled gases through a packed tower such as tower 3described above or the gas may be cooled to a lower temperature andscrubbed with water to absonb the mercuric chloride. The water solutionmay then be concentrated and 55 seconds. Under these conditions 47.0% oithe mercuric chloridewas reduced to metallic mercury and about 9.0percent oi the methane was chlorinated. The yield oi chloromethanesbased on the quantity oi methane and mercuric chloride reacted wasquantitative. 'The chlorinated product consisted of 87.3 percent methylchloride and 12.7 percent methylene chloride.

My invention makes possible a method ior chlorinating methane or naturalgas rich in methane wherein temperature conditions are easily controlledand the processmakes possible chlorination oi these gases without danger.oi creating an 1 explosive mixture oi hydrocarbon and chlorine. Theprocess also makes possible the reutilization oi hydrogen chlorideformed in the chlorination process.

1. The process ior the manufacture of at least one chloride of methaneirom methane which comprises maintaining said methane in contact with achlorinating agent consisting oi mercuric chloride vapor in a reactionzone at a temperature within the range oi from about 500 C. to about 650C. and fora contact time such that not more than percent of saidmercuric chloride is converted to metallic mercury and recovering saidchloride oi methane irom the gaseous eiiluent of said reaction zone.

2. The process for the manufacture oi achlorinated hydrocarbon whichcomprises passing a hydrocarbon gas stream consisting essentially oiparafllnic hydrocarbons of not more than two carbon atoms and comprisingnot more than 15 mole percent of ethane in contact with mercuricchloride vapor in a reaction zone at a temperature within the range offrom 500 C. to 650 C. for sufficient time to convert at least 35 percentand not more than 90 percent oi said mercuric 'chlochloride is formedand recovering said chlorinated hydrocarbon irom the gaseous eilluent oisaid reaction zone. I.

3. 'Ilhe process ior the manufacture oi a chlorinated hydrocarbon whichcomprises passing a hydrocarbon gas stream consisting essentially ofparailinic hydrocarbons oi not more than two carbon atoms and comprisingnot more than 15 mole percent oi ethane in contact with mercuricchloride vapor in a reaction zone at a temperature within the range oifrom about 500 C. to about 650 0., adjusting the contact time oi saidgas with the mercuric chloride vapor in said reaction zone to a numberoi seconds greater than represented ,by the expression Contact time=oI51o y-11.91) t and less than that represented by the expression Contacttimc=5.o 10 2- 1 1.91)

where T is the temperature in degrees Kelvin in said reaction zone, andrecovering said chlorinated hydrocarbon from the gaseous effluent ofsaid reaction zone.

4. The process for the manufacture of chloromethanes which comprisespassing a gaseous mixture of methane and mercuric chloride through areaction zone at a temperature within the range of from about 500 C. toabout 650 C. at a rate such that the contact time is sufficient toreduce at least 35 percent. and not more than 90 percent of saidmercuric chloride to free mercury, cooling the gaseous effluent from thereaction zone to a temperature below 500 C. and sumcient to condensemercuric chloride and metallic mercury therefrom, and recovering thechloromethane product.

5. The process for the manufacture of methyl chloride from methane andmercuric chloride which comprises the steps of (1) introducing a gaseousmixture consisting essentially of methane and mercuric chloride to achlorination zone at a temperature within the range of from about ,curyand hydrogen chloride of step 2 and hydrogen chloride introduced from anexternal source in contact with a free oxygen containing gas in aseparate reaction zone to regenerate mercuric chloride, (4) separatingmercuric chloride from the reaction product of step 3, (5) recycling theunreacted methane and unreacted mercuric chloride of step 2 and themercuric chloride of step 4 to the chlorination zone of 10 where T isthe temperature in degrees Kelvin maintained in said reaction zone toform a vapor mixture consisting essentially of unreacted methane,unreacted mercuric chloride, chlorinated .1 methane, hydrogen chloride,and free mercury;

(2) continuously fractionating the vapor mixture of step 1 to obtainseparate streams consisting essentially of unreacted methane, unreactedmercuric chloride, chlorinated methane, hydrogen chloride, and freemercury, (3) continuously passing the hydrogen chloride and free mercuryof step 2 in contact with a free oxygen containing gas in a separateregeneration zone whereby mercuric chloride is regenerated and watervapor is formed, (4) continuously separating the mercuric chloride fromthe water vapor of step 3, (5) recycling the unreacted methane andmercuric chloride of step 2 and the regenerated mercuric chloride ofstep 4 to step 1, and (6) recoveringchlorinated methane from step 2 ofthe process.

9. The process for the manufacture of at least one chloride of methanefrom methane and mercuric chloride which comprises the steps of (1)passing a, gaseous mixture consisting essentially of methane andmercuric chloride through a reaction zone packed with a refractory solidat a temperature withinvthe range of from about 500 C. to about 650 C.whereby said methane is chlorinated and hydrogen chloride is formed andat least percent of said mercuric chloride and not more than 90 percentof said mercuric chloride is reduced to free mercury, (2) fractionatingthe reaction product or step 1 to obtain separate streams of unreactedmethane, at least one chloride of methane, hydrogen chloride, unreactedmercuric chloride, and free mercury, (3) passing the free mercury andhydrogen chloride of step 2 and hydrogen chloride introduced from anexternal source in contact with a free oxygen containing gas in aseparate reaction zone packed step 1 of the process, and (8) recoveringsaid with a refractory solid at a temperature within the range of fromabout 500 C. toabout 650 C. to regenerate mercuric chloride whereby atleast a part of the exothermic heat of the reaction is stored in thepacking of said separate reaction zone, (4) separating mercuric chloridefrom the reaction product of step 3, (5) recycling the unreacted methaneand unreacted mercuric chloride of step 2'and the mercuric chloride ofstep 4 to the reaction zone of step 1, and (6) recovering said of atleast one chloromethane from methane which comprises the steps of (1)continuously passing a gaseous mixture of said methane and mercuricchloride th ough a reaction zone at a temperature within the range offrom about 525 C. to about 575 C. at a contact time in secondscorresponding to the expression chloride of methane from step 2 of theprocess.

10. The process as described in claim 9 wherein the processes of steps 1and 3 are carried out alternately in the same reaction zone whereby atleast a part of the heat stored in the reaction zone of step 3 isutilized in step 1 of the process. EVERETT GORIN.

REFERENCES CITED Country Date Great Britain Apr. 14, 1924 Number

